606 research outputs found

### A Comment on Technical Naturalness and the Cosmological Constant

We propose a model of dynamical relaxation of the cosmological constant.
Technical naturalness of the model and the present value of the vacuum energy
density imply an upper bound on the supersymmetry breaking scale and the
reheating temperature at the TeV scale.Comment: 10 pages, ref. adde

### Hybrid Inflation Exit through Tunneling

For hybrid inflationary potentials, we derive the tunneling rate from field
configurations along the flat direction towards the waterfall regime. This
process competes with the classically rolling evolution of the scalar fields
and needs to be strongly subdominant for phenomenologically viable models.
Tunneling may exclude models with a mass scale below 10^12 GeV, but can be
suppressed by small values of the coupling constants. We find that tunneling is
negligible for those models, which do not require fine tuning in order to
cancel radiative corrections, in particular for GUT-scale SUSY inflation. In
contrast, electroweak scale hybrid inflation is not viable, unless the
inflaton-waterfall field coupling is smaller than approximately 10^-11.Comment: 17 pages, 2 figure

### Signals of Inflation in a Friendly String Landscape

Following Freivogel {\it et al} we consider inflation in a predictive (or
`friendly') region of the landscape of string vacua, as modeled by
Arkani-Hamed, Dimopoulos and Kachru. In such a region the dimensionful
coefficients of super-renormalizable operators unprotected by symmetries, such
as the vacuum energy and scalar mass-squareds are freely scanned over, and the
objects of study are anthropically or `environmentally' conditioned probability
distributions for observables. In this context we study the statistical
predictions of (inverted) hybrid inflation models, where the properties of the
inflaton are probabilistically distributed. We derive the resulting
distributions of observables, including the deviation from flatness
$|1-\Omega|$, the spectral index of scalar cosmological perturbations $n_s$
(and its scale dependence $dn_s/d\log k$), and the ratio of tensor to scalar
perturbations $r$. The environmental bound on the curvature implies a solution
to the $\eta$-problem of inflation with the predicted distribution of $(1-n_s)$
indicating values close to current observations. We find a relatively low
probability ($<3%$) of `just-so' inflation with measurable deviations from
flatness. Intermediate scales of inflation are preferred in these models.Comment: 20 pages, 11 figure

### Complex Physics in Cluster Cores: Showstopper for the Use of Clusters for Cosmology?

The influence of cool galaxy cluster cores on the X-ray
luminosity--gravitational mass relation is studied with Chandra observations of
64 clusters in the HIFLUGCS sample. As preliminary results we find (i) a
significant offset of cool core (CC) clusters to the high luminosity (or low
mass) side compared to non-cool core (NCC) clusters, (ii) a smaller scatter of
CC clusters compared to NCC clusters, (iii) a decreasing fraction of CC
clusters with increasing cluster mass, (iv) a reduced scatter in the
luminosity--mass relation for the entire sample if the luminosity is scaled
properly with the central entropy. The implications of these results on the
intrinsic scatter are discussed.Comment: 6 pages; to appear in the proceedings of the conference Heating vs.
Cooling in Galaxies and Clusters of Galaxies, edited by H. Boehringer, P.
Schuecker, G.W. Pratt, and A. Finoguenov. Dedicated to the memory of Peter
Schuecke

### Generalized Second Law of Thermodynamics on the Event Horizon for Interacting Dark Energy

Here we are trying to find the conditions for the validity of the generalized
second law of thermodynamics (GSLT) assuming the first law of thermodynamics on
the event horizon in both cases when the FRW universe is filled with
interacting two fluid system- one in the form of cold dark matter and the other
is either holographic dark energy or new age graphic dark energy. Using the
recent observational data we have found that GSLT holds both in quintessence
era as well as in phantom era for new age graphic model while for holographic
dark energy GSLT is valid only in phantom era.Comment: 8 pages, 2 figure

### Dark Viscous Fluid coupled with Dark Matter and future singularity

We study effects of viscous fluid coupled with dark matter in our universe.
We consider bulk viscosity in the cosmic fluid and we suppose the existence of
a coupling between fluid and dark matter, in order to reproduce a stable de
Sitter universe protected against future-time singularities. More general
inhomogeneous fluids are studied related to future singularities.Comment: 11 page

### A New WIMP Population in the Solar System and New Signals for Dark-Matter Detectors

We describe in detail how perturbations due to the planets can cause a
sub-population of WIMPs captured by scattering in surface layers of the Sun to
evolve to have orbits which no longer intersect the Sun. We argue that such
WIMPs, if their orbit has a semi-major axis less than 1/2 of Jupiter's, can
persist in the solar system for cosmological timescales. This leads to a new,
previously unanticipated WIMP population intersecting the Earth's orbit. The
WIMP-nucleon cross sections required for this population to be significant are
precisely those in the range predicted for SUSY dark matter, lying near the
present limits obtained by direct underground dark matter searches using
cyrogenic detectors. Thus, if a WIMP signal is observed in the next generation
of detectors, a potentially measurable signal due to this new population must
exist. This signal, lying in the keV range for Germanium detectors, would be
complementary to that of galactic halo WIMPs. A comparison of event rates,
anisotropies, and annual modulations would not only yield additional
confirmation that any claimed signal is indeed WIMP-based, but would also allow
one to gain information on the nature of the underlying dark matter model.Comment: Revtex, 37 pages including 6 figures, accepted by Phys. Rev D.
(version to be published, including changes made in response to referees
reports

### CMB Power Spectrum from Noncommutative Spacetime

Very recent CMB data of WMAP offers an opportunity to test inflation models,
in particular, the running of spectral index is quite new and can be used to
rule out some models. We show that an noncommutative spacetime inflation model
gives a good explanation of these new results. In fitting the data, we also
obtain a relationship between the noncommutative parameter (string scale) and
the ending time of inflation.Comment: 8 pages, 2 figures; v2: refs. added and minor corrections; v3:
further minor correctio

### Topological Defects in an Open Universe

(To appear in Nuclear Physics B Supplements Proceedings section) This talk
will explore the evolution of topological defects in an open universe. The
rapid expansion of the universe in an open model slows defects and suppresses
the generation of CBR fluctuations at large angular scale as does the altered
relationship between angle and length in an open universe. Defect models, when
normalized to COBE in an open universe, predict a galaxy power spectrum
consistent with the galaxy power spectrum inferred from the galaxy surveys and
do not require an extreme bias. Neither defect models in a flat universe nor
standard inflationary models can fit either the multipole spectrum or the power
spectrum inferred from galaxy surveys.Comment: 11 pages and 4 figures, Elsevier Publisher's LaTeX, POP-54

### Light Neutralinos and WIMP direct searches

The predictions of our previous analyses about possible low-mass (lower than
50 GeV) relic neutralinos are discussed in the light of the most recent results
from WIMP direct detection experiments. It is proved that these light
neutralinos are quite compatible with the new annual-modulation data of the
DAMA Collaboration; our theoretical predictions are also compared with the
upper bounds of the CDMS and EDELWEISS Collaborations.Comment: 4 pages, 1 figures, typeset with ReVTeX4. The paper may also be found
at http://www.to.infn.it/~fornengo/papers/note.ps.gz or through
http://www.to.infn.it/astropart/index.htm

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